Switching power supply, EMI filter, common mode inductor and wrapping method for the common mode inductor

ABSTRACT

The present disclosure provides a switching power supply, an EMI filter, a common mode inductor and a wrapping method for the common mode inductor. The common mode inductor includes: a magnetic core; two multilayered coil windings symmetrically wrapped around the magnetic core; and two isolation gaps each of which is formed in respective one of the two multilayered coil windings, and is configured to divide, by beginning from a first layer, the respective one of the multilayered coil windings into two wrapping areas.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe prior Chinese Patent Application No. 201410240854.7 filed on Jun. 3,2014, entitled “SWITCHING POWER SUPPLY, EMI FILTER, COMMON MODE INDUCTORAND WRAPPING METHOD FOR THE COMMON MODE INDUCTOR”, before Chinese StateIntellectual Property Office, under 35 U.S.C. §119. The content of theabove prior Chinese Patent Application is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to the technical field ofElectromagnetic Interference (EMI) suppression, and more particularly,to a common mode inductor, a wrapping method for a common mode inductor,and an EMI filter and a switching power supply which use the common modeinductor.

BACKGROUND

A switching power supply is a power supply which maintains a stableoutput voltage by controlling a ratio of on-to-off time of a switch. Theswitching power supply products are developing towards a direction ofsmall type and high frequency, which results in difficulties inimprovement of EMI noise in switching power supply products. A commonmode inductor, as one of main components for suppressing EMI noise in aswitching power supply, self characters of which have obvious influenceon EMI noise suppression.

As shown in FIG. 1, an equivalent circuit diagram of a common modeinductor is illustrated. As shown in FIG. 2, a schematic structurediagram of a common mode inductor in conventional technologies proposedfor improving EMI noise suppression capability of a common mode inductoris shown. The common mode inductor mainly includes a magnetic core 102and two multilayered coil windings 101 (double-layered coil windingswith a first layer coil winding 101A and a second layer coil winding101B are shown in FIG. 2) symmetrically wrapped around the magneticcore. Furthermore, an isolation gap 103 is formed in each of themultilayered coil windings 101, and the isolation gap 103 is configuredto divide, by beginning from a second layer coil winding 101B, each ofthe multilayered coil windings 101 into two wrapping areas. That is, noisolation gap is formed in a first layer coil winding 101A, and there isan isolation gap formed in the second layer coil winding 101B.

However, the EMI noise suppression capability of this common modeinductor still needs to be enhanced, which hampers the development ofswitching power supplies towards a direction of small type and highfrequency.

SUMMARY

Aiming at least a part of the technical problems in the conventionaltechnologies, the present disclosure provides a common mode inductor forproviding better EMI noise suppression capability. Further, the presentdisclosure provides a wrapping method for a common mode inductor, an EMIfilter and a switching power supply which use the common mode inductor.

Other properties and advantages of the present disclosure will becomeclear from the detailed description below, or may be partly appreciatedby practice of the present disclosure.

According to a first aspect of the present disclosure, a common modeinductor is provided. The common mode inductor includes: a magneticcore; two multilayered coil windings symmetrically wrapped around themagnetic core; and two isolation gaps each of which is formed inrespective one of the two multilayered coil windings, and is configuredto divide, by beginning from a first layer, the respective one of themultilayered coil windings into two wrapping areas.

According to a second aspect of the present disclosure, a wrappingmethod for a common mode inductor is provided. The common mode inductorincludes a first multilayered coil winding and a second multilayeredcoil winding. The method includes the steps of: disposing two isolationblocking sheets at different positions of a magnetic core; wrapping thefirst multilayered coil winding around the magnetic core, wherein thefirst multilayered coil winding is divided into two wrapping areas byone of the isolation blocking sheets; and wrapping the secondmultilayered coil winding around the magnetic core, wherein the secondmultilayered coil winding is divided into two wrapping areas by theother one of the isolation blocking sheets, wherein the firstmultilayered coil winding and the second multilayered coil winding aresymmetrically wrapped.

According to a third aspect of the present disclosure, an EMI filter isprovided. The EMI filter includes an anti-EMI filter circuit composed ofresistors, inductors and capacitors which are coupled in series or inparallel. The inductors include the common mode inductor according tothe first aspect of the present disclosure.

According to a fourth aspect of the present disclosure, an EMI filter,including an anti-EMI filter circuit composed of resistors, inductorsand capacitors which are coupled in series or in parallel. The inductorsinclude the common mode inductor by use of the wrapping method accordingto the second aspect of the present disclosure.

According to a fifth aspect of the present disclosure, a switching powersupply is provided. The switching power supply includes the common modeinductor according to the first aspect of the present disclosure.

According to a sixth aspect of the present disclosure, a switching powersupply is provided. The switching power supply includes the common modeinductor by use of the wrapping method according to the second aspect ofthe present disclosure.

According to a seventh aspect of the present disclosure, a switchingpower supply is provided. The switching power supply includes the EMIfilter according to the first aspect of the present disclosure.

In the common mode inductor provided in the embodiments of the presentdisclosure, respective one of isolation gaps is formed in respective oneof multilayered coil winding, and then the respective one of themultilayered coil windings is divided, by beginning from a first layer,into two wrapping areas by using the respective one of the isolationgaps. The practices have proven that the present disclosure may greatlyimprove the EMI noise suppression capability of a common mode inductor,as compared with the technical solution in the conventional technologiesin which the isolation gap divides, by beginning from a second layercoil winding, one of the multilayered coil windings into two wrappingareas, and thereby the present disclosure may provide technical supportfor the development of switching power supplies towards the direction ofsmall type and high frequency

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present disclosurewill become clear from detailed description of exemplary embodimentswith reference to accompanying drawings.

FIG. 1 is an equivalent circuit diagram of a common mode inductor;

FIG. 2 is a schematic structure diagram of a common mode inductor inconventional technologies;

FIG. 3 is a schematic structure diagram of a common mode inductoraccording to an exemplary embodiment of the present disclosure;

FIG. 4 is a schematic flowchart showing a wrapping method for a commonmode inductor according to an exemplary embodiment of the presentdisclosure;

FIG. 5 is a schematic structure diagram of an isolation blocking sheetaccording to an exemplary embodiment of the present disclosure;

FIG. 6 is a schematic structure diagram after an assemblage of theisolation blocking sheet in FIG. 5 with a magnetic core;

FIG. 7 is a schematic structure diagram after a wrapping around themagnetic core in FIG. 6; and

FIG. 8 is a schematic structure diagram of a common mode inductorprepared using the wrapping method for the common mode inductor of thepresent disclosure.

DETAILED DESCRIPTION

Now, exemplary implementations will be described more comprehensivelywith reference to the accompanying drawings. However, the exemplaryimplementations may be carried out in various manners, and shall not beinterpreted as being limited to the implementations set forth herein;instead, providing these implementations will make the presentdisclosure more comprehensive and complete and will fully convey theconception of the exemplary implementations to the ordinary skills inthis art. In the drawings, thicknesses of areas and layers areexaggerated for the sake of clarity. Throughout the drawings similarreference numbers indicate the same or similar structures, and theirdetailed description will be omitted.

The features, structures or characteristics described herein may becombined in one or more embodiments in any suitable manner. In thefollowing description, many specific details are provided to facilitatesufficient understanding of the embodiments of the present disclosure.However, the ordinary skills in this art will appreciate that thetechnical solutions in the present disclosure may be practiced withoutone or more of the specific details, or by employing other methods,elements, materials and so on. In other conditions, well-knownstructures, materials or operations are not shown or described in detailso as to avoid confusion of respective aspects of the presentdisclosure.

Switching power supply products in conventional technologies aredeveloping towards a direction of small type and high frequency, whichresults in that a magnetic core in a common mode inductor cannot have anoverlarge diameter. As shown in FIG. 2, due to the restriction of thediameter of the magnetic core 102, if it is needed to wrap a coil with agreater number of turns and a fixed number of layers around the magneticcore 102, the number of turns in each layer shall be increased. When theisolation gap 103 is formed, on one hand, the number of turns of thecoil in other layers greatly depends on the number of turns of the coilin the first layer coil winding 101A; in order to wrap the greaternumber of turns of the coil, the number of turns of the first layer coilwinding 101A needs to be increased as far as possible without forming anisolation gap in the first layer coil winding 101A; on the other hand,even though an isolation gap 103 is formed in the first layer coilwinding 101A, the size of the isolation gap 103 is difficult to becontrolled during the wrapping procedure due to deformation resultedfrom wire jumping, which may result in instability in productproperties.

In an exemplary embodiment, a common mode inductor is provided byovercoming the above technical prejudice. As shown in FIG. 3, the commonmode inductor mainly includes a magnetic core 102, two multilayered coilwindings 101 (including a first multilayered coil winding 101X and asecond multilayered coil winding 101Y) symmetrically wrapped around themagnetic core 102 and two isolation gaps 103 each of which is formed inrespective one of the multilayered coil windings 101. Each of theisolation gaps 103 is configured to divide, by beginning from a firstlayer coil winding 101A, the respective one of the multilayered coilwindings 101 into two wrapping areas. The practices of the inventors ofthe present disclosure have proven that the present disclosure maygreatly improve the EMI noise suppression capability of the common modeinductor, as compared with the technical solution in the conventionaltechnologies in which each of the isolation gaps divides, by beginningfrom a second layer coil winding 101B, the respective one of themultilayered coil windings 101 into two wrapping areas. A part of theverification data is listed as follows.

Three groups (i.e., group A, group B and group C) of wrapping mannersare designed. It is required that impedances of magnetic cores used inthese groups do not greatly differ from each other. The number ofsamples in each group is 10 pcs (numbered as 1-10). One workerexperienced in wrapping is chosen to wrap three groups of samplesaccording to the specifications in Table 1.

TABLE 1 Group Group A Group B Group C Isolation gap No isolation gapWidth: 1 mm; Width: 1 mm; formed divides, by beginning divides, bybeginning from a second layer, from a first layer, a a coil winding intocoil winding into two two wrapping areas wrapping areas Wrapping Regularwrapping Regular wrapping Regular wrapping specificationsspecifications; specifications; specifications; stacking wrappingstacking wrapping stacking wrapping Total number 60 60 60 of turns (TS)

Impedances of the three groups of samples are tested under an inputsignal frequency of 500 KHz, and data in Table 2 is obtained as follows.

TABLE 2 Impedance of Impedance of Impedance of No. Group A (KΩ) Group B(KΩ) Group C (KΩ) 1 39.9 46.4 50.7 2 37.4 48.6 52.6 3 33.3 42.6 47.8 435.2 42.1 48.2 5 35.8 51.3 46.6 6 28.7 52.7 54.1 7 34.4 46.4 51.8 8 3045.3 49.4 9 30.6 45.6 48.1 10 40.6 49.2 51.7 Maximum Value 40.6 52.754.1 Minimum Value 28.7 42.1 46.6 Average Value 34.59 47.02 50.1

Impedances of the three groups of samples are tested under an inputsignal frequency of 800 KHz, and data in Table 3 is obtained as follows.

TABLE 3 Impedance of Impedance of Impedance of No. Group A (KΩ) Group B(KΩ) Group C (KΩ) 1 21 26.2 27.4 2 19.2 26.4 29.7 3 17.7 24 27.1 4 18.623.9 27.3 5 18.8 27.6 26.7 6 15.4 28.3 28.5 7 17.6 26.2 29.9 8 15.6 26.228.8 9 16.3 26.2 28.7 10 20.5 27.8 29.1 Maximum Value 21 28.3 29.9Minimum Value 15.4 23.9 26.7 Average Value 18.07 26.28 28.32

It is obvious that the inductor in the present disclosure (i.e., thesamples in Group C) may greatly improve the EMI noise suppressioncapability of the common mode inductor, as compared with the technicalsolution in conventional technologies (i.e., the samples in Group B) inwhich each of the isolation gaps divides, by beginning from a secondlayer coil winding 101B, the respective one of the multilayered coilwindings 101 into two wrapping areas.

It shall be pointed out that, although illustration is made in theexemplary embodiment using the example in which the multilayered coilwinding 101 is a double-layered coil winding, a width D of the isolationgap is 1 mm and the magnetic core is a closed-loop-shaped magnetic core,it have been proven that the following technical solutions may alsogreatly improve the EMI noise suppression capability of the common modeinductor, that is, the multilayered coil winding 101 is a triple-layeredcoil winding, a quadruple-layered coil winding or a coil winding withmore layers, the width D of the isolation gap is 2 mm or other widths(e.g., any width within 0.5 mm to 5 mm), the magnetic core is anon-closed magnetic core or the closed magnetic core is aclosed-polygon-shaped magnetic core or a closed magnetic core havingother shapes, and the isolation gap 103 divides, by beginning from thefirst layer coil winding 101A, one of the multilayered coil windings 101into two wrapping areas.

As described above, if it is intended to achieve the above common modeinductor by the wrapping method in conventional technologies, the mostpossible manner is to reserve an isolation gap by experience of workersafter they have wrapped the first wrapping area 1011, and then thesecond wrapping area 1012 is wrapped. However, during the wrappingprocedure, wires in the first layer coil winding may become saggy andthus the reserved isolation gap may deform as the advancing of thewrapping procedure, which will result in difficulties in controlling ofsize of the isolation gap, thereby lead to instability in productproperties.

Thus, in an exemplary embodiment, a wrapping method for a common modeinductor is further provided. As shown in FIG. 4, the wrapping methodfor a common mode inductor mainly includes the following steps.

In step S101, two isolation blocking sheets are disposed at differentpositions of a magnetic core.

In step S102, a first multilayered coil winding 101X is wrapped aroundthe magnetic core, wherein the first multilayered coil winding 101X isdivided into two wrapping areas by one of the isolation blocking sheets;a second multilayered coil winding 101Y is wrapped around the magneticcore, wherein the second multilayered coil winding 101Y is divided intotwo wrapping areas by the other one of the isolation blocking sheets.The second multilayered coil winding 101Y and the first multilayeredcoil winding 101X are symmetrically wrapped. It shall be noted that thepresent disclosure does not impose specific limitations on the wrappingsequence of the first multilayered coil winding 101X and the secondmultilayered coil winding 101Y.

In addition to the above steps, the method may further include StepS103.

In step S103, the isolation blocking sheets are taken off. It shall benoted that not taking off the isolation blocking sheets is alsoapplicable, which depends on actual conditions.

The above steps will be described in detail with reference to FIGS. 5˜8.

FIG. 5 is a schematic structure diagram of an isolation blocking sheetaccording to an exemplary embodiment of the present disclosure. As shownin FIG. 5, an isolation blocking sheet 104 has a “␣” shape. An openingwidth W of the isolation blocking sheet is substantially the same as athickness of the magnetic core, and thus the isolation blocking sheet104 may be assembled to the magnetic core in a snap-fit manner. As shownin FIG. 6, it is a schematic structure diagram after an assemblage ofthe isolation blocking sheet 104 with the magnetic core 102 in asnap-fit manner. It shall be noted that although the magnetic core 102shown is a closed-ring-loop-shaped magnetic core, the present disclosureis not limited to this and a closed-polygon-shaped (e.g.,rectangular-shaped) magnetic core or a closed magnetic core 102 havingother shapes is also applicable.

The material of the isolation blocking sheet 104 may be non-magneticmaterial (such as organic material or alloy material) which may becoupled to the magnetic core 102 in a snap-fit manner or may be adheredto the magnetic core 102. In addition, considering the magnetic materialof the magnetic core 102, the isolation blocking sheet 104 may also beformed of a magnetic material, i.e., the isolation blocking sheet 104 ismagnetic. Indeed, the isolation blocking sheet 104 may also be made byferromagnetic material. Thus, magnetic absorption force exists betweenthe isolation blocking sheet 104 and the magnetic core 102, such thatthe isolation blocking sheet 104 may be fitted onto the magnetic core102 by using this magnetic absorption force. Thus, the shape of theisolation blocking sheet 104 may be not limited to the above “␣” shape,but may also be a “L” shape or other shapes such as a “U” shape or a “C”shape or a swallow tail shape. For example, when the isolation blockingsheet has a relatively large thickness H, due to a large contact areawith the magnetic core 102, the applied force is more sufficient, thus,a “L” shape may be selected. When the isolation blocking sheet has arelatively small thickness H, a “U” shape may be selected to fix theisolation blocking sheet 104 by using a snap-fit force and a magneticabsorption force.

The thickness H of the isolation blocking sheet may be set depending ona size of the isolation gap to be formed. For example, a width of theisolation gap may be set as 0.5 mm˜5 mm. For example, if a width D ofthe isolation gap to be formed is 1 mm, the thickness H of the isolationblocking sheet needs to be set as 1 mm; if a width D of the isolationgap to be formed is 2 mm, the thickness H of the isolation blockingsheet needs to be set as 2 mm, and so on.

The isolation blocking sheet 104 may be of an integrated structure, andthe thickness of the isolation blocking sheet 104 may be determined whenthe isolation blocking sheet 104 is molded; or, for convenientadjustment of the thickness of the isolation blocking sheet 104, theisolation blocking sheet 104 may be constructed by stacking a pluralityof thin sheet structures. For example, when a thickness of every thinsheet structure is 0.5 mm and a 2 mm-isolation blocking sheet 104 isneeded, it only needs to stack four such thin sheet structures together.The connection manner between such thin sheet structures may be adhesiveconnections, or may be magnetic connections, and the present disclosuredoes not impose special limitations on this.

After the isolation blocking sheets 104 is disposed at preset positionsof the magnetic core 102, respective one multilayered coil winding maybe wrapped around respective one of two half-rings of the magnetic core102 respectively, and the number of layers, the wire diameter and thenumber of turns of the two multilayered coil windings are the same. Asshown in FIG. 7, a schematic structure diagram after wrapping is shown.It can be seen that, during the wrapping procedure, the isolationblocking sheets 104 may maintain the shape of the isolation gap so as toavoid deformation of the isolation gap, and the size of the isolationgap may be stably controlled by selection of the thicknesses of theisolation blocking sheets 104. In addition, with the leading andassistance of the isolation blocking sheets 104, it is more convenientfor wrapping operation, which brings benefits for increase of productionefficiencies.

As shown in FIG. 8, after completion of wrapping, the isolation blockingsheets 104 may be taken off, and then an isolation gap 103 having astable shape and a preset size is finally left. Thus, not only the EMInoise suppression capability of the common mode inductor is increased,but also stability in product properties is obtained. Indeed, theisolation blocking sheets 104 may not be taken off from the magneticcore 102 after completion of wrapping, so as to further ensure that theformed isolation gap 103 does not deform during usage of the common modeinductor and thus reliability of product performance is increased.

In an exemplary embodiment, an EMI filter is also provided. The EMIfilter includes an anti-EMI filter circuit composed of inductors,capacitors and resistors which are coupled in series or in parallel, andthe inductors include the above common mode inductor. Since the abovecommon mode inductor has enhanced EMI noise suppression capability, itis possible to provide better EMI noise suppression capability for theEMI filter, and less dependency on other EMI suppression components maybe achieved (e.g., the number of capacitors in the integrated filtercircuit may be reduced and the capacitance amount may be decreased).Consequently, the EMI filter may have a simple structure design, suchthat space and production costs may be saved, which brings benefits fordevelopment of the EMI filter towards a direction of small type and highfrequency.

In an exemplary embodiment, a switching power supply is provided. Theswitching power supply may be any power supply that is achieved bycontrolling on and off of a switch. For example, the switching powersupply may be an Uninterruptible Power System (UPS), a communicationpower supply or a welding power supply, etc. The switching power supplyin the present disclosure includes the above common mode inductor. Sincethe above common mode inductor has enhanced EMI noise suppressioncapability, it is possible to provide better EMI noise suppressioncapability for the switching power supply, and less dependency on otherEMI suppression components may be achieved (e.g., the number ofcapacitors in the integrated switching power supply may be reduced andthe capacitance amount may be decreased). Consequently, the switchingpower supply may have a simple structure design, such that space andproduction costs may be saved, which brings benefits for development ofthe switching power supply towards a direction of small type and highfrequency.

The present disclosure is described with the above exemplary embodimentswhich are only examples for implementing the present disclosure. Itshall be pointed out that the disclosed embodiments do not limit thescope of the present disclosure. Instead, modifications and variationswithout departing from the spirit and scope of the present disclosurefall into the protection scope of the present disclosure.

What is claimed is:
 1. A common mode inductor, comprising: a magneticcore; two multilayered coil windings symmetrically wrapped around themagnetic core, wherein each of the two multilayered coil windingscomprises a first layer immediately on the magnetic core and at leastone second layer on the first layer; and two isolation gaps, each ofwhich is formed in respective one of the two multilayered coil windings,and is configured to divide, by beginning from the first layer to the atleast one second layer, the respective one of the two multilayered coilwindings into two corresponding wrapping areas, wherein each of the twoisolation gaps is formed by an isolation blocking sheet which isdisposed between the two corresponding wrapping areas, and the isolationblocking sheet is detachable from the magnetic core.
 2. A switchingpower supply, comprising the common mode inductor according to claim 1.3. The common mode inductor according to claim 1, wherein each of theisolation blocking sheet has a thickness that is set depending on a sizeof the corresponding isolation gap to be formed.
 4. The common modeinductor according to claim 3, wherein each of the isolation blockingsheet has a width of 0.5 mm˜5 mm.
 5. The common mode inductor accordingto claim 1, wherein the two isolation gaps have a width of 0.5 mm˜5 mm.6. The common mode inductor according to claim 1, wherein the magneticcore is a closed-loop-shaped magnetic core or a closed-polygon-shapedmagnetic core.
 7. A wrapping method for a common mode inductor, having afirst multilayered coil winding and a second multilayered coil winding,the method comprising: disposing two isolation blocking sheets atdifferent positions of a magnetic core; wrapping the first multilayeredcoil winding around the magnetic core, wherein the first multilayeredcoil winding is divided into two wrapping areas by one of the twoisolation blocking sheets; and wrapping the second multilayered coilwinding around the magnetic core, wherein the second multilayered coilwinding is divided into two wrapping areas by the other one of the twoisolation blocking sheets, wherein the first multilayered coil windingand the second multilayered coil winding are symmetrically wrapped, andafter symmetrical wrapping the two multilayered coil windings around themagnetic core, the method further comprises: taking off the twoisolation blocking sheets.
 8. A switching power supply, comprising thecommon mode inductor by use of the wrapping method according to claim 7.9. The method according to claim 7, wherein the two isolation blockingsheets are magnetic or comprise a ferromagnetic material.
 10. The methodaccording to claim 7, wherein the two isolation blocking sheets are ofnon-magnetic materials, and the two isolation blocking sheets areassembled to the magnetic core in a snap-fit manner, or adhered to themagnetic core.
 11. The method according to claim 7, wherein the twoisolation blocking sheets have a “␣” shape or a “L” shape.
 12. Themethod according to claim 7, wherein the two isolation blocking sheetsare of an integrated structure or are constructed by stacking aplurality of thin sheet structures.
 13. The method according to claim 7,wherein the two isolation blocking sheets have a thickness that is setdepending on a size of a corresponding isolation gap to be formed. 14.The method according to claim 13, wherein each of the isolation gaps hasa width of 0.5 mm˜5 mm.